We have three hypotheses for our project. 1) First, that Testosterone treatment in men and DHEA treatment in men and women will have a mixed anabolic/anti-resorptive effect that leads to increased bone mass; 2) that Testosterone treatment in men not only affects bone turnover directly but also has indirect, extraskeletal effects that contribute to improved Ca homeostasis; 3) that androgens act directly on mature osteoblasts and regulate the expression of specific genes involved in osteoblast proliferation and differentiation. The specific aims of this study are to determine the effects of Testosterone treatment in men and DHEA treatment in men and women on BMD and markers of bone turnover; to determine the effects of Testosterone treatment on extraskeletal Ca metabolism in men; and to assess the direct effects of androgens on osteoblast proliferation and differentation, and on growth factor production.